1. Field of the Invention
The present invention relates to a thermal printer and more particularly to a thermal printer with which the uniformity of print density can be maintained. In particular, the present invention is directed a thermal printer provided with means for always maintaining the print density uniform even when there occurs any variation in the voltage of power source (for example, dry element battery, solar battery or other electric power source the output of which varies greatly).
2. Description of the Prior Art
In the above mentioned type of thermal printer, the print density becomes thinner with a decrease of the voltage of the battery used in the printer. Therefore, it has been a common practice to exchange an old battery for a new one before the print density has become very thin. However, frequent exchanges of batteries, especially at short intervals is troublesome to the operator.